<!DOCTYPE html>
<html lang="en">
    <head>
        <meta charset="UTF-8">
        <style>

            p{
                color:red;
                font-size:30;
            }
            .haha{
                font-size: 40px;
            }
            #a{
                 color:green;
            }

        </style>

    </head>
    <body>
        <p id="b">  这是一个段落标签</p>
        <img id ="a"src="./yajinzi.jpg" width="250" height="150px" border="5px">
        <a href="http://www.baidu.com" target="_blank"> 点击进入百度</a><br>

        //输入框里的值用value
        //标签里的用innerHTML
        <form  class="haha"     action="http://43.140.252.84:8889" method="post">
            id     <input  id="username" type="text" name="username"><br>
            passwd <input  id="passwd" type="password" name="password"><br>
            <input type="submit" value="提交" name="submit ">

        </form>
        <button onclick="test()">简单的按钮</button>
    </body>

    <script>
        function test()
        {
            var a=document.getElementById("b")
            alert(a.innerHTML);

            //
        }
    </script>
</html>